Forward genetics in Wolbachia: Regulation of Wolbachia proliferation by the amplification and deletion of an addictive genomic island.

Wolbachia is one of the most prevalent bacterial endosymbionts, infecting approximately 40% of terrestrial arthropod species. Wolbachia is often a reproductive parasite but can also provide fitness benefits to its host, as, for example, protection against viral pathogens. This protective effect is currently being applied to fight arboviruses transmission by releasing Wolbachia-transinfected mosquitoes. Titre regulation is a crucial aspect of Wolbachia biology. Higher titres can lead to stronger phenotypes and fidelity of transmission but can have a higher cost to the host. Since Wolbachia is maternally transmitted, its fitness depends on host fitness, and, therefore, its cost to the host may be under selection. Understanding how Wolbachia titres are regulated and other aspects of Wolbachia biology has been hampered by the lack of genetic tools. Here we developed a forward genetic screen to identify new Wolbachia over-proliferative mutant variants. We characterized in detail two new mutants, wMelPop2 and wMelOctoless, and show that the amplification or loss of the Octomom genomic region lead to over-proliferation. These results confirm previous data and expand on the complex role of this genomic region in the control of Wolbachia proliferation. Both new mutants shorten the host lifespan and increase antiviral protection. Moreover, we show that Wolbachia proliferation rate in Drosophila melanogaster depends on the interaction between Octomom copy number, the host developmental stage, and temperature. Our analysis also suggests that the life shortening and antiviral protection phenotypes of Wolbachia are dependent on different, but related, properties of the endosymbiont; the rate of proliferation and the titres near the time of infection, respectively. We also demonstrate the feasibility of a novel and unbiased experimental approach to study Wolbachia biology, which could be further adapted to characterize other genetically intractable bacterial endosymbionts.

Titer regulation in arthropod-Wolbachia symbioses.

Symbiosis between intracellular bacteria (endosymbionts) and animals are widespread. The alphaproteobacterium Wolbachia pipientis is known to maintain a variety of symbiotic associations, ranging from mutualism to parasitism, with a wide range of invertebrates. Wolbachia infection might deeply affect host fitness (e.g. reproductive manipulation and antiviral protection), which is thought to explain its high prevalence in nature. Bacterial loads significantly influence both the infection dynamics and the extent of bacteria-induced host phenotypes. Hence, fine regulation of bacterial titers is considered as a milestone in host-endosymbiont interplay. Here, we review both environmental and biological factors modulating Wolbachia titers in arthropods.

Insecticidal and sterilizing effect of Olyset Duo®, a permethrin and pyriproxyfen mixture net against pyrethroid-susceptible and -resistant strains of Anopheles gambiae s.s.: a release-recapture assay in experimental huts.

In the context of the widespread distribution of pyrethroid resistance among malaria vectors, we did a release-recapture trial in experimental huts to investigate the insecticidal and sterilizing effects of a novel long-lasting net (LN), Olyset® Duo, incorporating a mixture of permethrin (PER) and the insect growth regulator (IGR), pyri-proxyfen (PPF). An LN containing PPF alone and a classic Olyset® Net were tested in parallel as positive controls. The effect of progressive number of holes (6, 30, or 150) that may accrue in nets over time was simulated. We used two laboratory Anopheles gambiae s.s. strains: the susceptible Kisumu strain and the pyrethroid-resistant VK-Per strain having solely kdr as resistance mechanism. The effect of these nets on the reproductive success of blood-fed females that survived the different LNs conditions was recorded. Regardless of the mosquito strain, the LNs containing PPF alone with as many as 30 holes drastically reduced the number of eggs laid by females succeeding in feeding, i.e. fecundity by 98% and egg hatching rate (fertility) by 93% relative to untreated control net. Very few of the resistant females blood fed and survived under the Olyset® Duo with similar number of holes (up to 30) but of these few, the inhibition of reproductive success was 100%. There was no evidence that the Olyset® Duo LN with 150 holes impacted fecundity or fertility of the resistant colony. The efficacy of Olyset® Duo is encouraging and clearly illustrates that this new net might be a promising tool for malaria transmission control and resistance management.

Aedes (Stegomyia) aegypti (Diptera: Culicidae) in some islands of Cape Verde: Types of breeding sites and their relationship with larval presence / Aedes (Stegomyia) aegypti (Diptera: Culicidae) em algumas ilhas de Cabo Verde: tipologia dos criadouros e sua relação com a presença larval

Aedes aegypti is a species of wide geographical distribution, and its presence is registered on the islands of Cape Verde. Because its bioecology is being currently studied in several parts of the world, and since the first record of a dengue epidemic has been accomplished in the country, we decided to conduct this survey. The study was carried out between February and March, 2010, when six out of the ten islands of the archipelago were inspected. The factors evaluated during the survey were number, type and location of containers, as well as the presence of larval forms of Ae. aegypti. Results showed the existence of 2.4 containers/inspected houses, registering a total of 118 breeding sites, which are more common among abandoned buildings. The risk condition was significantly different between islands, being higher for Boa Vista. All evaluated islands showed a significant decreasing tendency of breeding sites, except for Fogo island (GLM; p 4; 0.05). The barrels were the containers most frequently recorded (> 50 L) (42.6%), located both inside and outside the houses. As breeding sites, barrels (> 50 L), tanks (> 200 L) and plastic tanks (> 50 L) were more common (t test; p 4; 0.05).

Aedes aegypti é uma espécie de ampla distribuição geográfica, e sua presença foi registrada nas ilhas de Cabo Verde. Pelo fato de a sua bioecologia estar sendo atualmente estudada em várias partes do mundo, e também por ter sido realizado o primeiro registro de uma epidemia de dengue no país, decidiu-se pela realização deste levantamento. O trabalho foi realizado entre fevereiro e março de 2010, quando foram inspecionadas seis das dez ilhas que compõem o arquipélago. Os fatores avaliados durante o levantamento foram número, tipo e localização dos recipientes, assim como a presença das formas larvais de Ae. aegypti. Os resultados demonstraram a presença de 2,4 recipientes/residência inspecionada, registrando-se um total de 118 criadouros, sendo estes mais frequentes nas residências abandonadas. A condição de risco foi significativamente diferente entre as ilhas, sendo superior para Boa Vista. Todas as ilhas avaliadas demonstraram tendência significativa à diminuição do número de criadouros, com exceção da ilha de Fogo (GLM; p 4; 0.05). Os recipientes mais frequentemente registrados foram os barris (> 50 L) (42.6%), localizados tanto no interior quanto no exterior das residências. Como criadouros, foram registrados com mais frequência os barris (> 50 L), tanques (> 200 L) e tanques plásticos (> 50 L) (Teste t; p 4; 0.05).